The beginning of 'Allhallowtide' or 'Hallowmas.' This night is the Evening ("Eve") of all the Holy (Hallow) Ones, ushered in by First Evensong for All Hallowed Ones, aka All Saints! All Hallow's Eve (Oct 31), All Saints (Nov 1), & All Souls (Nov 2) form a kind of 'Triduum for the Dead.'